I tried the game with my current system and a 22-23" syncmaster. the monitor shuts down after few hours if I play at high resolutions "tried another monitor and its the same".

oo hm, that could be a bunch of things really, maybe bad drivers or your GPU is dusty. i personally dont think it is worth it to upgrade your system right now, if it was working right you wouldnt see a very large performance upgrade in games as you should be playing them on max at 1080 as is. try and update your drivers, or roll back your drivers and clean out your case and gpu. if that isnt working then try and isolate the problem, is your computer crashing or just the monitor stops working? are you tracking your temperatures?